1 Field of the Invention
This invention relates to a process for producing vinegar having a high acetic acid concentration and, more particularly, to a process for producing vinegar having an acetic acid concentration higher than 18 percent weight by volume by a submerged fermentation process.
In the following specification and claims, without exception, the concentration of acetic acid is expressed in percent weight by volume and the concentration of alcohol in percent volume by volume, and the sum of percent weight by volume of acetic acid and percent volume by volume of alcohol is called total concentration.
2. Description of the Prior Art
Hitherto, various attempts have been made for obtaining vinegar having a high acetic acid concentration by a submerged fermentation. For example, in the process described in Published unexamined patent application (Kokai tokkyo koho) No. 52-15,899, vinegar having a high acetic acid concentration is obtained by a continuous batch process wherein the manner of alcohol feeding is improved and also in the processes described in Published unexamined patent application (Kokai tokkyo koho) Nos. 52-79,092; 53-41,495 and 53-44,696, productions of vinegar having a high acetic acid concentration are attempted by separating a multiplication tank from an acidification tank.
However, since in an acetic acid fermentation, as the acetic acid concentration becomes higher, the inhibition of the growth of acetic acid bacteria by acetic acid, which is the main product in the acetic acid fermentation, becomes severer, vinegar having an acetic acid concentration higher than 18 percent weight by volume has never been economically produced in an industrial process and hence there remain various matters to be improved in the acetic acid fermentation. Also, in the case of producing vinegar by a submerged fermentation process, as the fermentation temperature is higher, the production of vinegar having a high acetic acid concentration becomes more difficult. Hromatka et al report in "Enzymologia", Vol. 15, 337-350 (1953) that in the production of vinegar by a submerged fermentatiion, as the total concentration of a fermenting broth becomes higher, the optimum temperature thereof becomes lower, but the report is on the production of vinegar having acetic acid concentrations up to 12 percent weight by volume, and in the reported process, the growth rate of acetic acid bacteria becomes lower due to the low fermentation temperature, which results in reducing greatly the acidification rate and makes the process unpractical from an economical view point.